Sleeve-tuned band-pass tuner with variable coupling



H. T. LYMAN Nov. 1,7, 1959 sLEEvE-TUNED BAND-PASS TUNER WITH VARIABLE couPLING Filed June 12, 1957 FIG. 2

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Unitedv States Patent f' SLEEVE-TUNED BAND-PASS TUNER WITH VARIABLE coUPLnvG Y,

Harold T. Lyman, Milford, Conn., assigner to Aladdin Industries,`lncorporated, Nashville, Tenn., a Kcorporation of lllinos t Application June `12, 1957, Serial No. 665,262

s claims.. (Cl. S33- 70) This invention relates to tuners Ytor use at high radio or television frequencies. f t

One `object of the present invention is to provide la new and improvedy band-pass-tuner `which affords substantiallyuniformband width throughout an extremely wide tuning range.

A further object Vis toV provide a new and improved couplerv which is tunable by sleeve means adapted to envelop the coil of the coupler, and which provides for automatic variation of the degree of coupling inresponse to movement ofthe sleeve means. o p

Another object is to provide a new and improved band-pass tuner in which substantially constant band width is achieved over a wide tuning range in a relatively simple, low cost arrangement.`

Further objects and, advantages of the present invenwith the accompanying drawings, `inwhich:

Fig. 1` is a somewhat diagrammatic elevational view of a tuner to be described as' anillustrative,embodiment of the present invention.

tionwill appear from the following description, taken Fig. 2 is an enlarged longitudinal sectional view of one element of the tuner, taken generally along a line 2--2 in Fig.l l. c A I Fig. 3 isa somewhatdiagrammatic,.transverse sectional view, taken along a line 3 3 in Fig. v1.

l Fig. 4 is a greatly enlarged fragmentary longitudinal Fig. Sis' a'circuit diagr'amrshowing one `application of theillustrative tuner. Y H o As already indicated, Fig.- Al illustrates a tuner l1, which in this casevis adapted to be employed as a tunable Thus, for example, the tunerV 1 may be Vemployed as a coupling device'in a television receiver. adapted to cover the VHF (very high frequency) television channels in the band from 54.to 216 Y.megacycles v band pass coupler at high radio or'television frequencies. 2 i

Thus, the tuner 1 hastwo,tunedcircuits, an input 7"? circuit 2 and an output circuit 3;. The circuits 2 andy 3 are substantially identical, and asingle-description will serve for both. Thus, each ofthe tuned circuits 2 and 3 comprises a generally `helicalyinductance coil 4, which in this case, is substantially cylindrical in shape. shown to bestadvantage in Figs. 2 and 4, each coil 4 Vcomprises a llat ribbon-like conductor 5 which is suitably formed or mounted on an insulating tubular support -or coil form 6. Thus, the coil conductor 5 may be formed on the support 6 by suitable lcircuit printing techniques.

A dielectric coating or Vcovering 6a is Vapplied. to the coil '4 to insulate the coil conductor 5, for apurpose to be Vdiscussed in detail shortly. It will be noted that `the coil conductor 5 varies'`r in width alongthe length of the coil.V Thus, in Fig. 2, `the coil conductor 5, is

relatively narrow along the upper end of the vcoil 4, and is relatively wide along the lwer'end of the coil.' The coil 4l has first and4 second end terminal portions 7 and 8 .at .the 112126?. and lower. @.1148 thereeff. Pasto the Yarn ICC ^ Aof the coil 4 is mounted in an opening 9V formed in an insulating plate or other support 10.

As disclosed and claimed in the copending application of Harold T. Lyman, Serial No. 438,043,1iled June 2l, 1954, Aeach coil 4 is adapted to be tuned by a sleeve 11 which is slidably received around the coil and is'mov'able over the coil from one end to the other thereof Y in enveloping relation thereto. Thus, the sleeve 11 is movable over the coil 4 between the upper and lower ends 7 and 8. The elect of the moving sleeve 11 is to vary the effective inductance of the coil 4 between the sleeve I11V and the lower end terminal portion 8. Thus, the sleeve 11 and the coil 4 provide a two-terminal tuned circuit, with the sleeve as one terminal and the end 3 of thecoil as the other terminal. It will be `understood that the coil 4 is resonated by its own inherent or distributed capacitance, usually augmented by capacitances associated with the circuit connected to the tuner, such circuit capacitances including interelectrode capacitances of vacuum tubes or the like, for example.

The illustrated sleeve 11 has an internally reduced lower or head end portion 12 which is received around the coil 4 in closely fitting slidable relation thereto. `Although this closely litting portion 12 of the sleeve vcould be in direct conductive engagement with the coil lconductor 5, it is more advantageous to provide dielectric means between the sleeve portion 12 and the coil 4, "so that the coupling therebetween will be capacitive. In the illustrated embodiment, the insulating coating 6a A'provides the dielectric between the closely fitting sleeve portion 12 and thev coil 4. The provision of this dielectric eliminates electrical noise that might otherwise be 'produced by thesliding movement of the sleeve 11 along the coil 4.

'The illustrated sleeve 11 has an upper or tail end portion 13 which is of substantially greater `inside diameter than the head end portion 12 and thus is spaced outwardly from the coil 4 to a substantial extent.,` 'I'he end portion 13` encloses or envelops the inactive yportion of the coil 4 above the closely litting'slleeveportion 12. It has been found that the stepped construction of the sleeve 11', with the closely fitting head end portion '12 and the Voutwardly spaced tail portion 13, greatly improves the ligure of merit or Q of the coil,l as compared with an arrangement employing a tuning sleeve having a singleg'substantially uniform inside diameter. Thus, the stepped construction localizes the capacitive energy 'exchange at the closely iitting `portion 12 and largely prevents the passage of radio frequency currents along the inactive portion of the coil 4 within the tail portion 13 of the sleeve. The sleeve 1.1 has the effect of jgreatly reducing the effective inductance of the inactive portion of the `coil 4 within the, sleeve, so as to eliminate `any troublesome spurious resonances which might other- ,'wise beV caused by the inactive coil portion. `The tail -portion 13 yof the sleeve is spaced closely enough to the `coil to suppress spurious resonances, while maintaining xthe Q of the active portion of the coil between the sleeve Yand the lower end portion 8.

It would be possible to make a circuit connection to Patented Nov. 17, 1959 In the illustrated embodiment, this is brought or second sleeve 14 around the rst sleeve 11. To provide a dielectric between the sleeve 11 and the coupling electrode 14, an insulating. coating or covering 15 is provided on the outside of the sleeve 11. The length and position of the coupling sleeve 14 are such that at least a portion of the tuning sleeve 11 is within the coupling sleeve 14 throughout the range of movement of the tuning sleeve 11 along the coil 4. In this case, the coupling sleeve 14 is quite elongated, although it might be relatively short. The coupling sleeve 14 is positioned so that its lower portion is around the upper portion of the coil 4. Even when the tuning sleeve 11 is moved downwardly as far as possible toward the lower end 8 of the coil 4, the upper end of the sleeve 11 is within the coupling sleeve 14. On4 the other hand, when the tuning sleeve 11 is retracted to the upper end 7 of the coil 4, the lower portion of the sleeve 11 is within the coupling sleeve 14. Thus, substantial capacitive coupling is always produced between the coupling sleeve 14 and the tuning sleeve-11. Various mechanical arrangements may be provided for moving the tuning sleeve 11 along the coil 4. Thus, in the illustrated arrangement, each tuning sleeve 11 is adapted to be operated by an arm 16 mounted on a swingable or rockable member 17 which supports all of the arms 16. A ilexible resilient rod-like member 18 is employed to establish a connection between the arm 16 and the sleeve 11. It will be seen that the upper end of the rod 18 is soldered or otherwise connected to the arm 16, while the lower end of the rod 18 is suitably secured to an insulating disk 19 mounted on the upper end of the tuning sleeve 11.

The illustrated coupling sleeve 14 is supported by a pair of legs 20 extending between the lower end of the sleeve and the insulating plate 10. It will be seen that the legs 20 are connected to an outwardly projecting flange 21 at the lower end of the sleeve 14 and are spaced outwardly a substantial distance from the tuning sleeve 11.

In the illustrated arrangement, the two coils 4 of the input and output tuned circuits 2 and 3 are parallel to each other and are spaced apart a short distance. Thus, inherent inductive and capacitive coupling exists between the two coils. Thus, the tuner 1 may be employed as a tunable band pass coupler, as illustrated by the circuit diagram of Fig. 5. This circuit illustrates an application of the tuner 1 in which the tuner is employed as an interstage coupler in a television receiver or the like.

In' this case, the tuner 1 provides band pass coupling vbetween the output of a radio frequency amplifier 22 and the input of a superheterodyne mixer 23. It will be seen that the amplifier 22 takes the form of a vacuum tube or an equivalent amplifying device having an output electrode in the form of a plate or anode 24. The mixer 23likewise comprises a vacuum tube or equivalent device having an input electrode, shown as a control grid 2s.

Various circuit connections may be employed to and from the tuner 1. In this case, the two terminals of the input tuned circuit 2 are provided by the end portion 8 of the coil 4, and the coupling sleeve 14, which, in turn, is capacitively coupled to the tuning sleeve 11. The terminal portion 8 of the coil 4 is connected to the plate or output electrode 24 by a lead 26 with a trimming inductance 27 connected in series therewith. The trimmer coil 27 may be variously constructed, but may, for example, take the form of a few turns of wire which may be compressed or stretched to provide a variable trimming inductance. Power supply voltage may be fed to the anode 24 by a lead 28 connected to the upper end 7 of thecoil 4 in the tuned circuit 2. The lead 28 may be extended through the inside of the hollow tubular coil form 6 as indicated in Fig. 5. A radio frequency choke coil 29 may be connected between the lead 28 and a ground by acapacitorV 31.

As in the case of the input tuned circuit 2, the two terminals of the output tuned circuit 3 are provided by the end portion 8 of the coil and the coupling sleeve 14. The input electrode 25 of the mixer 23 is connected to the terminal portion 8 of the coil 4 by a lead 32 with a trimmer coil 33 in series therewith. The trimmer coil 33 may be similar to the trimmer coil 27. A return resistor 34 is conventionally connected to providea direct current path between the grid 25 and ground.

The inherent coupling between the coils 4 of the tuned circuits 2 and 3 may be enhanced by the provision of a coupling circuit 35 between the terminal sleeves 14 of the input and output tuned lcircuits 2 and 3. In this case, the coupling circuit 35 simply comprises acapacitor 36 and a small inductance 37 which are connected in series between the coupling sleeves 14 and a ground lead 38, lthe sleeves 14 being connected together by a lead 39. Thus, the capacitor 36 and the inductauce 37 are common to the input and output circuits 2 and 3. The values of the capacitance 36 and4 the inductance 37 may be such as to provide a suitable degree of coupling and a suitable variation in the degree of coupling due to the changing impedance of the elements 36 and 37 with frequency. For example, a value of approximately lifty micro-microfarads has been employed successfully for the capacitor 36. The inductance 37 may consist merely of the inherent inductance of the leads to the capacitor 36, or' may be augmented by a coil of a few turns. It is advantageous to proportion the capacitor 3'6 and the inductance 37 so that the series resonant frequencyV thereof is somewhat above the highest frequency to' be'covered.

The inherent coupling between the input and output circuits 2 and 3', and' the additional coupling provided by the common coupling circuit 35, do not alord uniform band width throughout the frequency range covered by the tuner 1. Suicient coupling for the desired band width may be provided in the upper portion of the frequency range, but the coupling will be itisuicient to provide similar ba'nd width at the lower end of the range. If the circuit 35 is adjusted to provide suicien't coupling at the lower end of the frequency range, the coupling and the bandwidth will be excessive at the upper end of the range.

To provide additional coupling between the tuned circuits 2 and 3 for the llower part of the tuning range, an inductive coupling link 40 is provided around the two coils 4 of the tuned circuits 2 and 3.' In this case, the link 40 comprises av single turn of wire, or other conductor, looped aroundV both coils, although the link might have multiple turns. The link 40is supported by insulating members 41 mounted on thelegs 20. It will be seen that the link-10i is spaced outwardly from the coils 4 so as toafford clearance for passage of the tuning sleeves 11. The link 40 is' disposed in intermediate relation to the ends 7 and 8 ofthe coils 4, so that'the sleeves 11 will pass into theV link 40 atan intermediate point in the range of movement' of the sleeves.

When the sleeves 11 are' withdrawn'from the link 40, the coils 4 will be tuned to the lower portion of the frequency range. This portion may correspond to the lower portion of the VHF television band, comprising channels 2-6. For this lower portion of the frequency range, the link 40 provides additional coupling between the coils 4 of the tuned circuits 2 and 3, so as to afford adequate coupling and suitably wide band width'.

W-hen thesleeves 11 are moved over the coil so as to enter the'link 40, the coils will'be tuned to thel upper portion of the frequency range, which may correspond to Ytheupper portion of the VHF television band, compris- `enter the'link in l.tuning the coils towardlthe upper portion of the frequency range.- In this way, excessive band width inthe upper eiidof the'range is avoided.

The link 40 also acts as a pair o'f interconnected elec.- trodes to provide additional capacitive coupling between the coils 4 of the tuned circuits 2 and 3 for the lower portion of the frequency range. VThis capacitive coupling is also largely nullified `when the, sleeves 11i-,enter the link, because of the relatively low impedance between the sleeves and ground. i i l',

' Thus, the coLop'erative arrangementof the link and thetuning sleevesis such Vtha'tthe degree of coupling between the tun'ed circuits is automatically varied by the movement of the sleeves, to provide substantially uniform band width throughout the tuning range. This highly advantageous result is achieved with a minimum of coniplexity, and at extremely low cost.

Various modifications, Valternative constructions and equivalents may be employed withoutdeparting from the true spirit'and scope of the invention as exemplified Yin the foregoing description and defined in the following claims.

I claim:

1. In a tuner, the combination comprising first and second similar generally helical coils disposed in generally parallel spaced-apart relation, first and second conductive tuning sleeves movable telescopically over said respective rst and second coils from one end thereof towardk the opposite end thereof for varying the effective inductance of each of said coils between the corresponding sleeve and said opposite end of said coil, each of said sleeves having an internally reduced end portion received over the corresponding coil in closely fitting slidable relation thereto, each of said coils having a dielectric covering thereon to `provide for capacitive coupling between said coil and the corresponding sleeve, each of said sleeves having a portion stepped outwardly internally from the corresponding coil and extending longitudinally from said internally reduced end portion of said sleeve, first and second annular coupling electrodes disposed around said respective first and second sleeves with dielectric means between each of said electrodes and the corresponding sleeve to provide for capacitive coupling therebetween, at least a portion of each of said sleeves being within the correspondingelectrode throughout the range of movement of said sleeve, an input terminal connected to said opposite end of said first coil, an output terminal connected to said opposite end of said second coil, a common return input and output terminal, a conductor connected between said first and second coupling electrodes, an inductor and a capacitor connected in series between said conductor and said returnterminal, and a continuous inductive link coil looped around both of said first and second coils to establish inductive coupling therebetween, said link coil being disposed along said first and second coils at an intermediate point -between the ends thereof and being spaced outwardly from said coils to afford passage for said sleeves through said link coil, said sleeves upon passing through said link coil being effective substantially to nullify the inductive coupling action thereof.

2. In a tuner, the combination comprising first and second generally helical coils having first and second ends, first and second conductive tuning sleeves received around said respective coils and movable telescopically therealong in enveloping relation thereto between said first and second ends for varying the effective inductance of each of said coils between the second end thereof and the corresponding sleeve, an input terminal connected to said second end of said first coil, an output terminal connected to said second end of said second coil, a common return input and output terminal, coupling means interconnecting said sleeves and including common coupling impedance means mutually connecting said sleeves to said return terminal to establish coupling between said coils for al1 positions ofsaid sleeves, and a link coil looped in commonaround said first andsecond coils intermediate the ends thereof and spaced outwardly therefrom for receiving,` saidy sleeves, said llink coil affording inductive coupling between said first and second coils, said sleeves being movable into vsaid link coil at an intermediate point in the range-of movement of said sleeves and thereupon being effective largely ytonullify the inductive coupling spective Afirst and second sleeve'srwith dielectric` means between each of said electrodes and the corresponding sleeve to provide for capacitivecoupling therebetween, at least a portion of each of said sleeves being opposite the corresponding electrode throughout the range of movement of said sleeve, an input terminal connected to said second end of said first coil, an output terminal connected to said second end of said second coil, a common return input and output terminal, a conductor connected between said first and second coupling electrodes, a capacitor connected between said conductor and said return terminal to provide coupling between said coils for allV positions of said sleeves, and a continuous inductive link coil looped around both of said first and second coils to establish inductive coupling therebetween, said link coil being disposed yalong said coils at an intermediate point between the ends thereof and being spaced outwardly from said coils to afford passage for said sleeves through said link coil, said sleeves upon passing through said link coil being effective substantially to reduce the inductive coupling action thereof.

4. In a tuner, the combination comprising rst and second generally helical coils having rst and second ends, first and second conductive tuning sleeves movable telescopically over said respective first and second coils between said ends lthereof for varying the effective inductance of each of said coils between the corresponding sleeve and said second end of said coil, dielectric means between each of said coils and the corresponding sleeve to provide for capacitive coupling therebetween, first and second coupling electrodes disposed adjacent said respective first and second sleeves with dielectric means between each of said electrodes and the corresponding sleeve to provide for capacitive coupling therebetween, at least a portion of each of said sleeves being opposite the corresponding electrode throughout the range of movement of said sleeve, an input terminal connected to said second end of said first coil, an output terminal connected to said second end of said second coil, a common return input and output termina-l, coupling impedance means mutually interconnecting said common terminal and said coupling electrodes to provide coupling between said coils for all positions of said sleeves, and a coupling element adjacent both of said first and second coils to establish coupling therebetween, said coupling element being disposed along said coils at an intermediate point between the ends thereof and being spaced outwardly from said coils to afford passage for said sleeves between said element and said coils, said sleeves upon passing therebetween being effective substantially to reduce the coupling action of said element.

5. In a tuner, the combination comprising first and second generally helical coils having first and second ends, first and second conductive tuning sleeves movable telescopically over said respective first and second coils between said ends thereof for varying the effective inldueta'nce of each of said coils between the corresponding lsleeve andV said' second end o`f said coil, dielectric means between' each of saidc'oils'- andthe corresponding sleeve to provide for' capacitive coupling-l ther'eb'etwee, rstl and second coupling electrodes disposed-adjacent said respective rst and second sleeves withy dielectric means between Aeach of-said electrodes and the' corresponding sleeve to provide' for capacitive coupling therebetween', at least a portion of each of said sleeves beingopp'site the corresponding electrode throughout the range df movement terme'cliate point between the ends thereof and being spaced outwardly from said rst and second coils to afford passage for said sleeves through said link coil, said sleeves upon passing through said link coil being effective sub stantially to reduce the inductive coupling action thereof.

References Cited in the file of this patent UN'ITED STATES PATENTS 1,798,012 Cohen et al Mar. 24, 1931 2,250,366 Frisbee July 22, 1941 2,477,693 Guanella Aug. 2, 1949 2,511,185 Ware June 13, 1950 2,641,708 Carlson June 9, 1953 2,645,718 Keizer July 14, 1953 2,753,530 Horvath July 3, 1956 2,786,945 Lyman Mar. 26, 1957 OTHER REFERENCES y Radiotronv Designers Handbook, by Langord-Smith, 4th ed., pub. by Wireless Press, page 418. 

